The present invention relates to a composite optical waveguide, a variable-wavelength laser, and a method of oscillating a laser.
As disclosed in JP-A 2004-157530 (Patent Document 1), a silica-based optical waveguide comprising a core of SiO2, SiON, SiOx, or the like and a clad of SiO2 or the like has been established as PLC (Planar Lightwave Circuit) technology because it has a propagation loss as low as 0.01 dB/cm to 0.05 dB/cm and is connectable to a SMF (Single-Mode optical Fiber) or a semiconductor laser (Diode Laser, LD) with a low loss. Such a silica-based optical waveguide has been applied to various optical devices such as an optical branching filter/multiplexer (Arrayed Waveguide Grating, AWG) in a wavelength division multiplex optical communication system and a splitter in FTTH (Fiber To The Home).
Meanwhile, in an Si-based optical waveguide comprising a core of an Si semiconductor or the like and a clad of SiO2 or the like, there is a considerably large difference of the refractive index between the core and the clad. Therefore, the Si-based optical waveguide shows a strong tendency to confine light in the core and has a minimum bend radius of only several micrometers. Accordingly, such an Si-based optical waveguide has prospects for remarkably reducing the size of optical devices.
In fact, an extremely fine AWG or a T-O (Thermo-Optical) optical switch using an Si-based optical waveguide has been produced by way of trial.
Furthermore, since an Si-based optical waveguide comprises a core of semiconductor silicon, it can provide an E-O (Electro-Optical) device by application of an electric field or supply of an electric current.
In fact, an optical modulator using an Si optical waveguide has been produced with use of the above effect by way of trial, as disclosed by William M. Green, Michael J. Rooks, Lidija Sekaric, and Yurii A. Vlasov, “Ultra-compact, low RF power, 10 Gb/s silicon Mach-Zehnder modulator,” Optics Express, Vol. 15, Issue 25, (2007) pp. 17106-17113 (Non-Patent Document 1). Furthermore, an optical attenuator has been produced with use of the above effect by way of trial, as disclosed by H. Nishi et al., SSDM2009 Extended Abstract, 1-1-2, (2009) (Non-Patent Document 2).
Patent Document 1 suggests use of a combination of an Si-based optical waveguide and a silica-based optical waveguide.